1. Field of the Invention
The present invention relates to the field of solidified fluid surface treatment and more particularly to methods and apparatus for creating ice pellets for use in ice blasting applications, and methods and apparatus for ice blasting.
2. Description of the Prior Art
Prior art apparatus for creating particulate ice for use in ice blasting applications has traditionally relied upon coating a rotating drum with a thin layer of water or other working fluid, permitting the water to solidify, and fracturing off the solid water to form the desired ice particles. An example of this conventional technology can be found in U.S. Pat. No. 5,913,711.
As noted in the referenced patent, common problems associated with conventional technology relate to non-uniform particle size, conduit blockages, clump formation, etc. A significant reason for these problems relates to the means by which the particles are formed, namely, by fracturing thin sheets of ice. This process results in particles having a predominantly rectilinear geometry. These forms of ice are more susceptible to delivery problems than are pellets. One need only to look to nature to see that ice crystals and flakes have a significant tendency to clump, while pellets or other pseudo-spherical formations such as hail does not. Moreover, the aerodynamic properties of flakes are inferior to those of pellets. Consequently, the velocity of fractured ice is much more difficult to maintain after it has left a conduit.
Heretofore, there has been no convenient and low cost means for creating ice pellets for use in blasting or other similar applications.
The present invention concerns methods and apparatus for creating and using solidified fluid particles, particularly for treating various surfaces, commonly referred to as ice blasting. While the term xe2x80x9cicexe2x80x9d is used herein throughout, that term is intended to encompass all forms of solidified fluids resulting from a phase change from fluid to solid. The term xe2x80x9cworking fluidxe2x80x9d then represents the fluid that undergoes the phase change from fluid to solid. In addition, the term xe2x80x9cbubblexe2x80x9d is synonymous with a water column or fountain.
Apparatus in accordance with the invention comprise a frame to which a curved surface such as a drum is rotationally mounted wherein the drum comprises an outer peripheral surface. A cryogenic component is employed for causing the outer peripheral surface to reach a temperature (Ts) sufficient to cause a working fluid in contact therewith to solidify over a period of time. The cryogenic component may be ducted to the internal portions of the drum or directed to the outer peripheral surface.
Also mounted or linked to the frame is a fluid droplet applicator, which is in fluid communication with a source of the working fluid wherein the applicator defines a plurality of orifices through which the working fluid may be expelled and wherein the orifices are in close proximity to the outer peripheral surface of the drum. To facilitate removal of the solid particles, a particle removal member comprising a blade for example, is positioned adjacent to the outer peripheral surface of the drum.
Methods in accordance with the invention comprise establishing a temperature (Ts) on an outer peripheral surface of a rotatable curved surface such as a drum where (Ts) is sufficient to cause a working fluid to reach a solid phase in an ambient environment. The drum is further rotated either prior to or during the application of a plurality of fluid droplets to the outer peripheral surface of the drum. Upon contacting the outer peripheral surface of the drum, the droplets are permitted to substantially solidify into solid phase particles, where after the particles are removed.
One of many advantages the invention has over the prior art is the ability to create dense yet relatively smooth particles or pellets from a fluid. These attributes beneficially enhance the abrasive and sustained velocity characteristics of a blasting applicator using the resultant particles. Thus, particles produced according to the invention can be siphon fed or pressure fed in blasting equipment. Heretofore, the irregular and rectilinear shape of ice particles produced according to the prior art have made it very difficult to engage in high velocity blasting of target surfaces and use of the same in pressure feed blasting equipment. Thus, a system for blasting a target surface comprises the previously described apparatus and an enclosure wholly surrounding the apparatus, a container for receiving removed particles, and an outlet conduit in fluid communication with the container and an external portion of the container wherein the enclosure is selectively pressurized, thereby causing migration of any particles in the container to the external portion of the enclosure via the conduit. From there, conventional blasting equipment can be employed. Naturally, siphon feed systems can be employed as will be appreciated by those skilled in the art.
A preferred embodiment of the apparatus includes a conventional cryogenic fluid generating system wherein the fluid is introduced into an inner chamber defined by the drum and circulated therein. Conduction causes heat to migrate from the outer peripheral surface of the drum into the circulating fluid, thereby causing the surface temperature (Ts) to drop approximately to the temperature (Tf) of the cryogenic fluid. The target temperatures (Ts) and (T
f) depend upon the type of working fluid being applied to the surface of the drum. When fresh water is being used as the working fluid, (Ts) is approximately xe2x88x9228xc2x0 C. and (Tf) is approximately xe2x88x9237xc2x0 C.
The preferred embodiment utilizes internal cooling of the drum to achieve surface cooling thereof. Alternatively, the outer peripheral surface temperature (Ts) of the drum can be modified externally. Thus, a cryogenic gas or fluid can be applied directly to the surface (such as by directed exposure or immersion), or thermocouples integrated with the drum can be used to achieve the desired level of surface cooling.
While a preferred embodiment has the outer peripheral surface being smooth, modifications of the surface are considered within the scope of the invention. Thus, the nature of the formed pellets or particles can be modified by altering the physical characteristics of the surface.
Another feature of the preferred embodiment is the use a foramenous tube that functions as the fluid droplet applicator. This tube, preferably oriented adjacent to and congruent with the drum axis, delivers the working fluid to the drum. Because the mode of droplet application is preferably by means of bubbling, any suitable fluid conduit having a plurality of orifices positioned proximate to the drum surface will meet the requirements of the invention. Thus, the droplet applicator can be in accordance with the preferred embodiment, or may have discrete fluid sub-conduits extending from a common manifold. Moreover, the location of the applicator is preferably at the lowest portion of the drum to enhance the geometric properties of the particles to be formed. However, the location of the applicator is not limited to the preferred location.